A reduction gear device attached to a joint of an industrial robot, that reduces the number of revolutions applied to an input shaft, and that causes the revolution of a member that comprises a part located to the anterior of the joint is known to the art. This reduction gear device must have a large speed reducing capacity while being compact, comprises an external gear and an internal gear having a differing number of teeth than the external gear, and utilizes the phenomenon of the internal gear and the external gear revolving relative to one another when the external gear that is meshed with the internal gear revolves eccentrically. The basic configuration thereof is set forth in Japanese Patent Application Publication No. S62-218087. The reduction gear device set forth in Japanese Patent Application Publication No. S62-218087 comprises a crankshaft that, by means of rotation, causes an eccentric cam to revolve eccentrically, and an external gear that engages with the eccentric cam, the eccentric cam revolving eccentrically when the crankshaft is rotated, whereupon the external gear revolves eccentrically.
In the case where the rotation of the external gear is not allowed, the internal gear rotates around a center axis of an output shaft. Conversely, in the case where the rotation of the internal gear is not allowed, the external gear rotates while revolving orbitally around the center axis of the output shaft. The number of rotations applied to the input shaft can be reduced and can be transmitted to the output shaft by means of transmitting the rotation of the internal gear or the external gear to the output shaft.
It is often the case that an industrial robot has a plurality of joints and that each joint utilizes a reduction gear device. An industrial robot having a reduction gear devices attached to joints is set forth in Japanese Patent Application Publication No. S63-185595. The industrial robot set forth in Japanese Patent Application Publication No. S63-185595 has three joints at wrist portions of robot arm, and three reduction gear devices are built into these wrist portions.
FIG. 4 shows a schematic diagram of an industrial robot 30. The industrial robot 30 has a first joint 31, a second joint 32, a third joint 33, a fourth joint 34, a fifth joint 35, and a sixth joint 36. That is, the industrial robot 30 operates with the revolutionary movement of six shafts being combined.
The first joint 31 is fixed to an installing face, and is capable of rotating around a center axis CL1. The second joint 32 is capable of rotating around a center axis 38. The third joint 33 is capable of rotating around a center axis 40. The fourth joint 34 is capable of rotating around a center axis CL2. The fifth joint 35 is capable of rotating around a center axis 42. The sixth joint 36 is capable of rotating around a center axis CL3, a robot hand (not shown) is fixed to an anterior end of the sixth joint 36, by which work (an object being worked upon) is moved or processed.
A reduction gear device is built into each of the joints 31, 32, 33, 34, 35, and 36. The first joint 31, the second joint 32, and the third joint 33 are termed to be the three basic shafts of the industrial robot 30. The fourth joint 34, the fifth joint 35, and the sixth joint 36 are termed to be the three wrist shafts of the industrial robot 30, and form an anterior end part of a base part arm 52 of the robot. The fourth joint 34 comprises a reduction mechanism that reduces the number of revolutions of a motor 46 attached to a shoulder part 44 and causes a member located at the anterior side of the fourth joint 34 to rotate around the center axis CL2. The fifth joint 35 comprises a reduction mechanism that reduces the number of revolutions of a motor 48 attached to the shoulder part 44 and causes a member located at the anterior side of the fifth joint 35 to rotate around the center axis 42. The sixth joint 36 comprises a reduction mechanism that reduces the number of revolutions of a motor 50 attached to the shoulder part 44 and causes a member located at the anterior side of the sixth joint 36 to rotate around the center axis CL3.
FIG. 5 shows a diagram of a torque transmitting circuit of the three wrist shafts of the industrial robot 30. The motor 50 is not shown.
The torque of the motor 46 is transmitted to a hollow shaft 14 via a spur gear 14a. The hollow shaft 14 passes through the base part arm 52 of the robot, the torque is transmitted therethrough to the reduction gear device of the fourth joint 34, and causes the member at the anterior side of the fourth joint 34 to revolve in the direction of an arrow 41.
The torque of the motor 48 is transmitted to a hollow shaft 15 via a gear 15a. The hollow shaft 15 passes through the hollow shaft 14, and transmits the torque to a gear 15b. The gear 15b is orthogonal to and meshes with a gear 15c, and the direction of revolution between the gear 15b and the gear 15c is changed by 90 degrees. The torque transmitted to the gear 15c is transmitted to the reduction gear device of the fifth joint 35, and causes the member at the anterior side of the fifth joint 35 to revolve in the direction of an arrow 43.
The torque of the motor 50 (not shown) is transmitted to a shaft 17 via a gear 17a. The shaft 17 passes through the hollow shaft 15, and transmits the torque to a gear 17b. The gear 17b is orthogonal to and meshes with a gear 17c, and the torque transmitted to the gear 17c is transmitted to a spur gear 17e by a spur gear 17d that is fixed to the gear 17c. The direction of revolution is changed by 90 degrees when the torque is transmitted from the gear 17b to the gear 17c. The torque transmitted to the gear 17e is transmitted to a gear 17f that is fixed to the gear 17e and is orthogonal to and meshes with a gear 17g. The direction of revolution is changed by 90 degrees when the torque is transmitted from the gear 17f to the gear 17g, and the direction of revolution of the gear 17g becomes the same as the direction of revolution of the motor 50. The torque transmitted to the gear 17g is transmitted to the reduction gear device of the sixth joint 36, and causes the member at the anterior side of the sixth joint 36 to revolve in the direction of an arrow 45.